The present invention relates to semiconductor devices, and more particularly to techniques for the fabrication of semiconductor devices in 32 nm technology nodes and beyond.
The use of metal materials as gate conductors with high-k dielectrics has become prevalent in high-k metal gate (HKMG) process technology nodes at 32 nm and below (e.g., 28 nm). The use of aluminum or aluminum alloy for metal gate electrodes has cost and performance advantages so that aluminum gates have been widely used. The chemical mechanical polishing (CMP) process of aluminum gates is a very important process for manufacturing high-k metal gate transistors.
In order to increase the gap filling space, an aluminum gate CMP process is typically implemented in two steps: a CMP process for N-type aluminum gate transistors and a CMP process for P-type aluminum gate transistors.
In the process of performing CMP on the aluminum gate of a P-type transistor, a polishing pad can have simultaneously contact with the aluminum gate of the P-type transistor, the polysilicon gate of the polysilicon gate transistor, the dummy gate (typically polysilicon) of the NMOS transistor, and the interlayer dielectric layer. Since a conventional CMP process utilizes a polishing slurry that has a polysilicon removal rate greater than the aluminum removal rate, the polysilicon gate tends to be over-polished. Furthermore, an over-polishing of polysilicon gate may occur during the CMP process of the aluminum gate of the N-type transistors.
Thus, prior art techniques of removing the metal gate using a CMP process face the problems of over-polishing since the slurry of the CMP polishing has a polysilicon removal rate greater than the removal rate of a metal material (e.g., aluminum), leading to excessive over-polishing of the dummy gate and the polysilicon gate and a decrease in performance of a semiconductor device.
In view of the foregoing, there is a need for a novel method and apparatus for manufacturing a semiconductor device that can overcome the deficiencies of the prior art.